1. Field of the Invention
The present invention relates to a solid polymer electrolyte that is suitable for a fuel cell that generates electricity by humidifying an electrolyte membrane, and a fuel cell containing the same.
2. Description of the Background
As environment pollution increases, developments in clean energy have drawn much attention around the world. For example, since the number of automobiles has increased due to increased transportation traffic networks, the air pollution resulting from the exhaust gas that is generated from internal-combustion engines of cars has been a problem. In response to this problem, electric cars and hybrid cars that include fuel cells may be used because they are lightweight, can be handled easily, and do not pollute the air. In addition, fuel cells may also be used at home.
Fuel cells may be divided into categories including alkali fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid electrolyte fuel cells, solid polymer fuel cells and the like, depending on the type of electrolytic solution used. In particular, solid polymer fuel cells draw attention as an energy source for electric automobiles and use at home, for example because solid polymer type fuel cells may be handled easily at low temperatures and exhibit large output density.
Proton conductive membranes may be used as electrolytes for solid polymer fuel cells. Proton conductive membranes have high ionic conductivity with respect to protons that are involved in the reactions at electrodes of fuel cells. Conventionally, fluorinated polymers that include a superacid group may be used as proton conductive membranes. However, fluorinated polymers that include a superacid group are expensive and must be humidified because the medium for proton conductivity is water.
In order to have proton conductivity, an ionic group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, or the like may be included in an aromatic structure, which is disclosed in Japanese Patent Nos. 2002-280019 and 2002-358978. In this case, however, these ionic groups are easily released at high temperatures, have damage flexibility of proton conductive membranes, and have low proton conductivity. Although Japanese Patent No. Hei 8-504293 also discloses the above-related components, proton conductivity is not mentioned.
In addition, a method of introducing an active hydrogen group by reacting polybenzimidazole with sultone is disclosed in “Development of Ionic Exchanging Membrane for Solid Polymer Fuel Cell” GMC Co. Ltd., p. 98, May 2000. In this case, however, only a sulfonic acid group may be introduced, and other active hydrogen groups may not be applied.